I have written two small test games using DirectX 9. One uses
presentParams.Windowed = false;
presentParams.PresentationInterval = D3DPRESENT_INTERVAL_ONE;
and the other one uses
presentParams.Windowed = false; // same results with true
presentParams.PresentationInterval = D3DPRESENT_INTERVAL_IMMEDIATE;
Both use exactly the same window position, size and style. Both are written to cover the screen completely, even when using "Windowed = true".
In the latter game, to vsync and avoid tearing, my code waits until a certain scan line is passed. My tests showed: On different PCs it has to wait for different scan lines to avoid tearing completely. This is a drawback, since it has to be tweaked individually by the user. Is this technique used in any games?
And, compared to this technique, why does DirectX produce a display lag when "Windowed = false" is used with D3DPRESENT_INTERVAL_ONE?
To clarify where the lag occurs:
Windowed = false + INTERVAL_ONE => LAG
Windowed = false + ...IMMEDIATE => no lag
Not mentioned in the question but tested:
Windowed = true; + INTERVAL_ONE => no lag, tearing
Windowed = true; + ...IMMEDIATE => no lag